This invention lies in the field of motor control. More particularly it concerns the control of a small motor used as the timing basis for a sonar depth locator.
In the present day sonar depth locators, which are used by fishermen, the instruments are extremely portable and low power and operate generally from a twelve volt battery which may vary in voltage over a relatively wide range. The depth is usually indicated by the rotation of a D.C. motor. Once each revolution of the motor, a first voltage pulse is generated by a rotating magnet cooperating with a fixed induction coil. This first voltage pulse initiates the outgoing sonar pulse. When the sonar pulse returns after reflection at an object, a second voltage pulse is generated. There is a small neon lamp on a rotating flasher scan disc, and the first and second pulses cause flashes of the neon lamp. The angular spacing between the two flashes is a measure of the time of travel, or of the distance of travel, of the sonar pulse. Any variation in speed of the motor will change the angle between the two pulses and therefore will change the indicated distance. It becomes important, therefore, to provide a control on the motor speed so as to maintain it as nearly constant as possible irrespective of varying voltage, and conditions of load torque, friction, wear and temperatures.
It is a primary object of this invention to provide a simple electronic motor speed control that can be used with portable sonar instruments.